Porphyrin ring oxidation occurs in some heme-containing proteins, for example as part of the catalytic function of cytochrome P-450, peroxidases, and in heme catabolism. This study examines the role of the central metal, particularly iron, and porphyrin structure in the kinetic and equilibrium processes associated with porphyrin ring oxidation. Three polyphenolic porphyrins will be synthesized, tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphine (1-H2P) and its diphenolic analogs in which the phenol groups are trans (2-H2P) and cis (3-H2P). They will be characterized by FTIR, UV-vis, HNMR and CNMR. All three porphyrins combine quinone and porphyrin functionalities. The results from studies of these porphyrins and their metal derivatives will have implications for the behavior of both porphyrins and sterically-strained quinones. The two-electron oxidation products obtained by electrochemical or chemical oxidation of 1-H2P or a metal derivative such as 1-ZnP are quinone-like but have quite different properties. It is proposed that this difference arises because the central metal constrains oxidation to the cis-quinone while the more stable trans-quinone forms in the metal-free case. Electrochemical and chemical oxidation of 2-H2P and 3-H2P will provide a direct test of this hypothesis. The electrochemical methods to be used for studying the porphyrins, their metal derivatives, and the oxidation products derived from them include cyclic voltammetry, coulometry, and spectroelectrochemistry. Chemical oxidation of the porphyrins and their metal derivatives by CuCl2 in DMF will provide quantitative kinetic evidence for the influence of the metal and the role of substituent symmetry. Rate constants will be obtained by UV-vis spectrophotometry under pseudo-first order conditions. Since 1-Fe(III)P undergoes self-reduction in the presence of 1-methylimidazole, the effect of this added ligand will be studied. A considerable rate enhancement should be observed since 1-Fe(II)P should form a Pi-cation more readily. This prediction is based on electrochemical results that indicate a decrease in the potential for Pi-cation formation as the electrostatic interaction between metal and porphyrin decreases. The existence of such an oxidation pathway may account for the relative ease of in vivo Pi-cation formation.